International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Index Copernicus Value (2013): 6.14 | Impact Factor (2013): 4.438
The Corrosion Inhibition of Mild Steel in 0.5m
Phosphoric Acid and Crown Cork in Water By Folic
Acid
K. J. Orie1, A.O James2, O. Akaranta3
1, 2, 3
Department of Chemistry, University of Port Harcourt, Nigeria
Abstract: The corrosion inhibition of mild steel in 0.5M H3PO4 solutionand crown cork in water by folic acid was investigated using
weight loss experimentat different temperature (300C, 400C, 500C). The finding indicates that, folic acid acts as an effective corrosion
inhibitor for mild steel in phosphoric acid solutionand crown cork in water at 100C. The inhibition process was attributed to the
formation of an adsorbed film of inhibitor on the surface of mild steel which protect the metal from corrosion. The inhibition efficiency
and surface coverage of mild steel increased with increasing concentration of folic acid, but reduced as temperatureincreases. The
kinetic treatment of the results confirms a first order reaction kinetics with respect to corrosion of mild steel in 0.5M H 3PO4 andthe
crown cork in waterin the present of folic acid. The adsorption isotherm model which was determined from the results obtained from
weight loss experiment performed on mild steel coupon in phosphoric acid solution fits the Langmuir model. The inhibitive ability of
folic acid was attributed to the presence of oxygen, nitrogen and aromatic pyrimidine in its structure.
Keywords: Corrosion, Folic acid, Inhibition, Mild steel, Phosphoric acid.
1. Introduction
Mild steel is an alloy of iron that contains the following
elements and percentages: Carbon (0.05 – 0.15%), Silicon
(0.18%), Phosphorous (0.04%), Sulphur (0.02%),
Manganese (0.70 – 0.48%), and Iron, the rest of the
composition (about 98.9%) [1]. Mild steel remains one of
the alloy that is heavily sort for in the industry because of its
essential nature. One of the most challenging and difficult
task for industries are the protection of mild steel from
corrosion [2, 3]. Corrosion is a serious problem that
continues to be a great threat to the relevance of metals in a
wide range of industrial applications and products. This is
because it results in the deterioration and eventual failure of
component and system both in processing and
manufacturing industries [4].
Acid media are always used in the study of corrosion of mild
steel owing to the fact that acids (HCl, H 2SO4, H3PO4, etc.)
are commonly used for pickling, industrial cleaning,
descaling etc. [4]. Corrosion damages resulted from
exposure of metals to these media lead to decrease in
functional Properties of materials. In the effort to mitigate
mild steel from corrosion, various methods have been
employed, such as upgrading materials, blending of
production fluid, process control and chemical inhibition [5].
A number of chemical inhibitors [6-8] are known to be
applicable as good corrosion inhibitors of metals, but the use
of chemical inhibitors is depleting, due to strict
environmental regulation and toxic effect of the chemical
compound on human and animal life. Hence, there is need to
develop a new class of corrosion inhibitors with low
toxicity, eco-friendliness, good efficiency, acceptability and
low cost etc [9]. A lot of natural products were previously
Paper ID: 18091501
used as corrosion inhibitor for different metals in various
environments [10-15] and there optimum concentrations
were reported [16]. Theirsuccess indicates that the plant
extract could serve as effective corrosion inhibitors. It has
also been established that corrosion inhibition occurs via
adsorption of the organic molecule in these natural products
on the corroding metal surface. And that the efficacy of the
corrosion inhibition depends on the mechanical, structural
and chemical nature of the adsorption layer formed under
particular condition. Extracts of plant material contain a
wide variety of organic compounds; most of them contain
heteroatoms such as P, N, S& O [17]. These atom coordinate
with the corroding metal atom (their ion), through their
electron and prevent corrosion by formation of protective
layer on the metal surface [18, 19].
The purpose of the study is to reveal the use of folic acid to
combat the corrosion of mild steel in phosphoric acid at
different temperature and crown cork immersed in 100C cold
water at a given period.
Folic acid is an organic compound with the molecular
formula C19H19N7O6, relative molecular mass of 441.0,
solubility in water is 1.6mg/l at 250C and melting point
2500C. Folic acid is a synthetic form of folate which is a
generic form of a naturally occurring family of B group
vitamins which contain an aromatic pteridine ring linked to
P-amino-benzoic acid and one or more glutamate
residue[20]. Folic acid is found naturally in variety of food
including green leaf, vegetable, fruit, liver, and yeast.It is
also used for food supplement [20].
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International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Index Copernicus Value (2013): 6.14 | Impact Factor (2013): 4.438
Figure 1: Structure of Folic acid
Some of the functional group in the structure of folic acid
are:
1) Carboxylic acid ( - COOH)
2) Amide (- CONH2)
3) Amine (- NH2)
4) Hydroxyl – (OH)
5) Hetrocyclic containing nitrogen
the World Bank engineering workshop, university of PortHarcourt, Choba, Port-Harcourt. The crown corks used for
this study were obtained from Coca-Cola bottling company,
Trans-Amadi Industrial layout, Port-Harcourt. Cleaning and
degreasing was done with high grade acetone followed by
rinsing with distilled water.
2.2 Corrosive Medium
Due to of the presence of nitrogen, oxygen and heterocyclic
aromatic pyrimidine in the structure of folic acid, it is
imperative that folic acid can be used as an organic inhibitor
of mild steel in phosphoric acid. Folic acid has been vastly
use in medicine for curative purposes, the essence of the
paper is to diversify the use of folic acid in the industry.
Folic acid is environmentally safe, and so the advantage of
using folic acid as corrosion inhibitor is for both economic
and environmental benefits. Mild steel was chosen in the
study because of its vast application in the industries while
crown cork is used in breweries industries.
0.5M concentration of phosphoric acid was used as
corrodent to explore inhibition potential of different
concentration of folic acid. Thereafter water was used as a
corrodent in order to test the inhibitive efficiency of folic
acid on crown cap.
2.3 Preparation of test Solution
The inhibitor, folic acid was purchased from the
pharmaceutical store. The following masses (0.005g, 0.010g,
0.015g, 0.020g and 0.025g) were each dissolved in 100ml of
distilled water.
2.4 Weight Loss Measurement
Figure 2: Crown cork bottle cap.
Crowncorks get corroded when refrigerated (i.e in cold
andhigh humidity environment) and its corrosion inhibition
becomes very necessary. Hence, this study aims at inhibiting
the corrosion of mild steel and crown cork using folic acid.
2. Methods
2.1 Preparation of Mild Steel Coupon and the Crown
Cork
Different weighted mild steel specimens were immersed in
50ml of 0.5M of phosphoric acid and 50ml of different
concentration of folic acid (1.13 x 10 -4m, 2.27 x 104M, 3.4 x
10-4M. 4.54 x 10-4, and 5.67 x 10-4M). All the different
concentration of folic acid are mixed respectively with 50ml
of 0.5M of phosphoric acid in beaker and mild steel coupon
allowed to stay for the intervals of 30minutes for a duration
of 4hours (240minutes) before the mild steel coupons was
reweighed.
The experiment was carried out at different temperature of
30oC, 40oC and 50oC. The weights of the mild steel coupons
were recorded in order to determine the weight loss of the
metal. Inhibition efficiency was calculated using the
equation:
The commercial mild steel of thickness 1.0mm with a
dimension of 3 by 3mm used for this study was obtained at
The percentage inhibition efficiency =
Paper ID: 18091501
W Blank - W Inhibitor
W Blank
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x 100...........................(1)
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1381
International Journal of Science and Research (IJSR)
ISSN (Online): 2319-7064
Index Copernicus Value (2013): 6.14 | Impact Factor (2013): 4.438
Surface coverage is an important parameter to known the
interaction of inhibitor with mild steel surface, it was
determined using the formula:
𝜃 =
Wo – W1
………………. (2)
Wo
Where Wo and Wi are weight loss of mild steel in blank and
inhibitor solution respectively. Corrosion rate of mild steel is
a measure of the effectiveness of inhibitor and directly
related with weight loss in corrosive medium for estimated
period. It was computed from the following formula:
Cr =
87.6W
……………………… (3)
td
2.5 Method of Determining Corrosion Inhibition in
Crown Cork
The folic acid concentration that gave highest percentage
inhibition in mild steel - phosphoric acid experiment was
used to test corrosion inhibition of folic acid on crown cork
at 100C. Weighted crown cork was immersed in 5.67 x 104
M of folic acid solution and blank solution of water and
allowed for 14days. The crown cap was weighted at interval
of one day and the weighted loss was recorded.
3. Results and Discussion
Where Cr is corrosion rate in mm/yr, w – weight loss per
unit area of specimen, t – exposure time, and d – density of
mild steel (density of mild steel 7.85gcm-3).
Table1: Corrosion Parameter for mild steel in 0.5M H3PO4 with different concentration of folic acid at different temperature
Inhibition
concentration
1.1 3x10-42.27x10-4
3.40x10-44.45 x 10-45.67 x10-4-
Surface
Coverage
0.4368
0.6607
0.8544
0.9079
0.9600
Time
(days)
0
4
7
11
14
Time
(days)
0
4
7
11
14
30oC
Corrosion rate
1.76
1.04
0.46
0.29
0.12
%I
43.68
66.67
87.44
90.79
96.00
Surface
Coverage
0.3864
0.6275
0.8240
0.8795
0.9313
40oC
Corrosion
rate
1.87
1.14
0.54
0.37
0.27
50oC
Surface Corrosion rate
Coverage
0.3549
1.94
0.5932
1.12
0.7921
0.63
0.8561
0.43
0.9220
0.23
%I
38.64
62.76
82.40
87.95
93.13
Table 2: Crown cork in cold water without folic acid at 10oC
Initial weight
W1
0.072
0.072
0.072
0.072
0.072
Final weight
WF
0.072
0.068
0.065
0.063
0.062
Weight
loss∆𝑊
0
0.007
0.007
0.009
0.010
Change in weight
W1-∆W
0.070
0.065
0.065
0.063
0.062
Log
W1∆W
-1.1427
-1.1675
-1.1871
-1.2007
-1.2076
Table 3: Crown Cap in cold water with 5.67x10-4M folic acid at 10oC
Initial weight
W1
0.068
0.068
0.068
0.068
0.068
Final weight
WF
0.068
0.067
0.066
0.065
0.064
Weight
loss∆𝑊
0
0.001
0.002
0.003
0.004
Change in weight
W1-∆W
0.068
0.067
0.066
0.065
0.064
Log W1-∆W
-1.1675
-1.1739
-1.1805
-1.1871
-1.1938
%I
35.49
59.32
73.21
85.61
92.20
%
Inhibition
%
Inhibition
100
85.71
71.42
66.67
60.00
Table 1 shows the variation of surface coverage, corrosion
rate and efficiency of inhibition at 30oC, 40oC and 50oC
respectively. Increase in concentration of inhibitor lead to
increase in surface coverage, decrease in corrosion rate and
increase in percentage inhibition. It is also evident from
table 1 that increase in temperature decreases the surface
coverage and does not favour the inhibition by the folic acid.
Table 2 displays the variation of the weight loss of crown
corkin cold water without folic acid at 10oCwithin the
duration of 14days. Prolong exposure increases the weight
loss. The variation of weight loss in crown cap in water with
5.67x10-4M of folic acid at 100c is portrayed in table 3. The
weight loss in table 2 is greater than the one in table 3. This
drastic reduction in the weight loss indicates the inhibitory
action of folic acid.
Paper ID: 18091501
Figure 3: Variation of weight loss with time for mild steel
coupon in 0.5M solution containing different concentration
of folic acid at 30oC
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Figure 4: Variation of weight loss with time for mild steel
coupon in 0.5M solution containing different concentration
of folic acid at 40oC
Figure 5: Variation of weight loss with time for mild steel
coupon in 0.5M solution containing different concentration
of folic acid at 50oC
Figure 7: Variation of Log (W1-∆W) with time for mild
steel coupon in 0.5M of H3PO4 solution with different
concentration of folic acid at 40oC.
Figure 8: Variation of Log (W1-∆W) with time for mild
steel coupon in 0.5M of H3PO4solution containing different
concentration of folic acid at 50oC.
Figure 9: Variation of inhibitor efficiency with inhibitor
concentration for mild steel coupon in 0.5M solution
containing folic acid at three different temperatures
Figure 6: Variation of Log (W1-∆W) with time for mild
steel coupon in 0.5M of H3PO4 solution with different
concentration of folic acid at 30oC
Paper ID: 18091501
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3.1.1 Inhibitory Action of Folic acidon the corrosion of
mild steel in 0.5M H3PO4
Figs. 3-5 shows that folic acid is a corrosion inhibitor for
mild steel in 0.5M phosphoric acid solution, since there was
a general decrease in weight loss at the end of the corrosion
monitoring process at the temperature studied.
Figure 10: Variation of inhibitor efficiency with inhibitor
concentration for crown cork in 0.5M solution containing
folic acid at three different
From the variation of weight loss with time of exposure of
mild steel in 0.5M H3PO4 (blank) at 30oC (fig. 3) compared
with those containing inhibitors, there is a remarkable
decrease in weight loss which indicates that corrosion
inhibitor is effective. At 40oC, fig 4, shows reduction in
weight losses of mild steel coupon when the concentration
of folic acid is increased within the range of 1.13x10 -4M to
5.67x10-4-M. Fig. 5also shows a reduction in weight losses
of mild steel coupon at 50oC. This depicts that at high
temperature of 500C, folic acid can still offer some inhibitive
properties.
3.1.2 Effect of temperature on the inhibition efficiency
of folic acid
Fig. 9 shows the effect of increase in temperature on the
inhibition efficiency of folic acid. From the graph, it is
obvious that as the temperature increases from 30 – 50oC,
the inhibitory efficiency decreases.
Figure 11: Variation of weight loss with time for crown
cork in water solution containing 5.67x10-4M of folic acid
inhibitor at 100c.
Figure 12: Variation of Log (W1-∆W) with time forcrown
cork in water with different concentration of folic acid
inhibitor at 100c.
Figure 13: Langmuir Isotherm adsorption of folic acid on
mild steel in 0.5M H3PO4.
Paper ID: 18091501
3.1.3 Kinetic treatment of weight losses of mild steel
coupon in 0.5M H3PO4
Figs. 6-8show the variation of log (wi-∆w) with time for
mild steel coupon in 0.5M H3PO4 solution containing
different concentration of folic acid at different temperature
(30– 50oC). The initial weight loss of mild steel coupon at
time (t) is represented with W1, weight losses are ∆w, and
the weight change at t1 is (wi --∆w). The plot of log (wi-∆w) against time at the temperatures studied showed a linear
variation which confirms a first order reaction kinetics with
respect to corrosion of mild steel in 0.5M H3PO4 in the
present of folic acid.
3.1.4 Inhibitory action of folic acid on the corrosion of
crown cap in water at 100c
Fig 10 shows that folic acid is a corrosion inhibitor of crown
cap in water at 10oC. From the graph (fig 10) there was a
general weight losses in crown corkimmersed in water at
10oC without and with the presence of folic acid. The weight
loss difference between blank and solution containing
5.67x10-4M of folic acid reveals the inhibitive ability of folic
acid (fig. 11). Fig. 12 shows a linear variation of first order
reaction kinetics when log (w1 - ∆w) was plotted against
time for exposure in days.
3.1.5 Adsorption Studies
The Langmuir adsorption isotherm can be expressed by C/Ɵ
= 1/K – C. Where inhibition concentration is C, the fraction
of the surface covered Ɵ, adsorption coefficient kads. The
linear graph between C/Ɵ versus C in fig. 13 show that folic
acid obeys the Langmuir isotherm at the concentration and
temperature of the metal. It supports the assertion that the
mechanism of corrosion inhibition is due to the formation
and maintenance of a protective film on the metal surface
and the additive covers both the anode and cathode sites
through uniform adsorption following Langmuir isotherm.
The inhibitory action of folic acid should be attributed to the
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adsorption of its component on the mild steel surface. The
presence of N, O, C = O, N-H, C-O, -OH and N-hetero
cyclic ring in folic acid are responsible for the inhibitive
effect of folic acid.
4. Conclusion
Folic acid is an effective inhibitor of corrosion of mild steel
in phosphoric acid.The oxygen, nitrogen atom and aromatic
pyrimidinein it are electron rich and served as good
adsorption site on the mild steel surface. These are
responsible for inhibitory action of folic acid.Its inhibition
efficiency decreased, as the temperature increases, which
indicates that physical adsorption predominate mechanism
of inhibition.The adsorption fits the Langmuir adsorption
model. Folic acid also inhibits the corrosion of crown cork
in waterin cold environment (about 10oC). Since folic acid is
a relatively cheap, non-toxic effective corrosion inhibitor, it
can be applied in bottling company to reduce the extent of
corrosion in crown cork during their storage in refrigerator.
This will likely eliminate the corrosion product depositat the
tip of the bottle when consumers open the bottle. Some of
the limitation that this inhibitor might face is the operating
condition (i.e high temperature and pressure). Therefore, it
should not be exposed to condition that will denature the
molecule of folic acid and reduce its effectiveness as
corrosion inhibitor.
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